Wide angle lens system

ABSTRACT

A wide angle lens system includes 10 lenses in which the third, fourth and fifth lenses and the sixth, seventh and eighth lenses are cemented to form respective first and second triplet substems, the system satisfying the following conditions: F/0.9&lt; F1 &lt;F/0.6, F1 &lt;0 F/0.95&lt; F1.2 &lt;F/0.57, F1.2 &lt;0 5F&lt; F2 F/2.3 &lt;F1.2 . . . 8 &lt;F/1.65 F/1.3 &lt;F1.2 . . . 9 &lt;F/1.05 0.25F &lt; r13 &lt;0.37F, r13 &lt;0 0.5F &lt; r15 &lt;0.6F, r15 &lt;0 0.1 &lt;N4 - N5 &lt;0.2 0.12F &lt;r7 &lt;0.2F Nu 6 - Nu 7 &lt;0.6 0.05 &lt;n8 - n7 &lt;0.15 0.18 &lt; R11 &lt;0.26F, r11 &lt;0 Wherein F is the focal length of the entire system, F1.2 . . . i is the focal length of the subsystem including the first to the i th lens, Fi is the focal length of the i th lens, Ni is the dline refractive index of the i th lens, Nu i is the Abbe&#39;&#39;s number of the i th lens, and rj is the radius of curvature of the j th lens surface, cemented confronting lens faces defining a single surface.

Takahashi U llllcu DI,

[ WIDE ANGLE LENS SYSTEM [75] lnventor: Yasuo Takahashi, Tokyo, Japan [73] Assignee: Asohi Kogaku Kogyo Kabushiki Kaisha, Tokyo-t0, Japan 221 Filed: Mar. 26, 1973 [21] Appl. No.: 345,145

[30] Foreign Application Priority Data Mar. 28, 1972 Japan 47-30975 [52] US. Cl. 350/215, 350/176 [51] Int. Cl. G02b 9/62 [58] Field of Search 350/214, 215, 176, 177

[56] 1 References Cited UNITED STATES PATENTS 3,154,628 10/1964 Bertele 350/215 X 3,630,600 12/1971 Bertele 350/215 Primary Examiner-John K. Corbin A 45W 9! i m w s stsis 959 s ABSTRACT A wide angle lens system includes 10 lenses in which July 23, 1974 the third, fourth and fifth lenses and the sixth, seventh and eighth lenses are cemented to form respective first and second triplet substems, the system satisfying the Wherein F is the focal length of the entire system, F is the focal length of the subsystem including the first to the i th lens, F, is the focal length of the i th lens, N, is the d-line refractive index of the i th lens, 11, is the Abbes number of the i th lens, and r, is the radius of curvature of the j th lens surface, cemented confrontinglens faces defining a single surface.

1 Claim, 5 Drawing Figures PATENIEB' M23 I974 I 3.825.321

FIG. 20' FIG. 2b FIG. 2c

I I I I I I I I I I I I I I I I -d-LINE -L|NE I L A. 1 l 1 l I -o.1 o 0.1 -o.1 o 0.1 -.o.1-/. o 0.1% -o.1 o 0.1 SPHERICAL ABERRATION CHROMATIC DISTORTION ASTIGMATISM SINE CONDITION ABERRATION WIDE ANGLE LENS SYSTEM The present invention relates generally to improvements in lens systems and it relates particularly to an improved wide angle lens system.

The conventional wide angle lens system generally possess optical properties which leave much to be desired. They are usually characterized by high distortions and aberrations and are of a nature which inhibits adequate compensation and correction of these optical drawbacks.

it is thus a principal object of the present invention to provide an improved lens system.

Another object of the present invention is to provide an improved wide angle lens system.

Still another object of the present invention is to provide a highly distortion free wide angle lens system.

The above and other objects of the present invention will become apparent from a reading of the following description taken in conjunction with the accompanying drawing which illustrates a preferred embodiment thereof.

In a sense the present invention contemplates the provision of a highly distortion free wide angle lens system including ten consecutively designated lenses, the third, fourth and fifth lenses being cemented together to form a first triplet subsystem and the sixth, seventh and eighth lenses being cemented together to form a second triplet subsystem, the lens system satisfying the following conditions (I) through (IX):

Wherein F is the focal length of the entire system, F is the focal length of the subsystem including the first through the ith lens, F is the focal length of the ith lens, N, is the d-line refractive index of the ith lens, 11, is the Abbes number of the ith lens, and r, is the radius of curvature of the jth lens surface, cemented lens faces defining a single surface. The first, fourth, sixth, eighth, ninth and lOth lenses are negative, the third, fifth and seventh lenses are positive and both triplet subsystems are positive.

The conditions to be satisfied by the present improved lens system according to the present invention and their application are hereinafter described inv detail.

The condition (I) serves to prescribe the power of the first lens and is a general requirement in the wide-angle lens system in order that the following groups do not involve any wide angle requirements. It is possible in the present lens system to employ a first lens of smaller dimension by providing this first lens with substantially high power since a lens of lower power is used as the second lens. When F, is shorter than F/0.9, however, the effect of size reduction and light amount increase is improved on one hand, and a Petzvals sum is reduced and coma aberration is intensified on the other hand. Compensation of this inconvenience by the other on the third and the following lenses becomes less significant with a result that compensation of various types of aberration in the following groups would be difficult.

The condition (ll) serves to prescribe the power not only of the subsystem comprising the first and the second lenses but also of the second lens itself. When F 9 is near to F/0.9, F shorter than F/0.95 would bring about the disadvantages previously mentioned with respect to the condition (I). When F is longer than F/0.6, F longer than F/O.57 would also result in that the effect in the preceding groups becomes less noticeable and compensation of various types of aberration is difficult. The function of F however, lies in suitable control of .any difference between distortion occurring on the third and the fourth surfaces.

The condition (III) is to prescribe the power of the ninth lens in association with the condition (IV) and influences upon compensation of distortion aberration in association with the condition (V), as well. The condition (III) will be explained in relation with the other types of aberration. Although, when F 8 is shorter than F/2.3, P I 9 may be properly compensated in the proximity of F/ l .3, the overall compensation would be easily unbalanced since the positive spherical aberration occurring on the 12th surface would be large, compensation thereof would be difficult and the Petzval 5 sum would diminish; When F 9 is shorter than F/ l .3, the burden on the 10 the lens would increase and the coma aberration would be readily aggravated. F

, 9 being made longer than F/ 1.05, however, would now increase the burden on the ninth lens. When F 8 is longer than F/ 1.65, it would be difficult for the I such as spacings and lens thickness cannot be neglected. The power of the ninth lens is thus defined by the foregoing conditions.

The condition (V) is to prescribe r and enables a proper compensation of distortion aberration on this surface in association with the foregoing conditions. This will now be described with respect to each type of aberration. When r is shorter than 0.25F, the spherical aberration which has occurred and has been compensated only to an extremely insufficient extent on the 12th surface would be compensated in excess of the balance. With respect to the distortion, there is a possibility that this could not be sufficiently compensated on the 14th surface. When m is longer than 0.37F on the contrary, the spherical aberration would remain insufficiently compensated while the distortion could not be easily compensated on the 14th surface.

The condition (V1) is to enable a proper compensation of any distortion occurring on the 16th surface of the lOth lens on the assumption that the lens has no appreciable power.

The condition (Vll) serves to prescribe the refractive power at the seventh surface and is effective for compensation of spherical aberration and sine condition. in

' view of the fact that the seventh surface preferably has no influence upon the oblique light rays, the difference of refractive indices should be properly limited within the range from 0.1 to 0.2. The difference of refractive indices lower than 0.1 would interfere with compensation of spherical aberration and sine condition and such a compensation could not be accomplished unless r is greater than 0.12F. On the other hand, the difference of refractive indices higher than 0.2 would require r, to be less than 0.7F and possibly have an adverse influence upon the oblique light rays.

The condition (VIII) is to indicate means by which the coma aberration is compensated independently of the chromatic aberration, wherein the difference of v values in excess of 10.6 would unsuitably increase the variation of coma aberration which depends upon the particular colors. I

The condition (IX) is to compensate the spherical aberration in the direction of excessive compensation especially without any influence upon the ther types of aberration such as distortion. Even when r is shorter than O.l8F, the other types of aberration would be adversely influenced insofar as the difference of refractive indices is not higher than 0.05. On the contrary, when the difference of refractive indices is higher than 0.15, even r being higher than 0.26F would increase the refractive power, substantially affecting the other types of aberration.

The improved wide angle lens system is of very low distortion as is evidenced by its aberration curves and provides excellent optical performance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a wide angle lens system embodying the present invention; and

FIGS. 2(a) to 2(d) are curves illustrating the aberration characteristics of the lens system.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing which illustrates a preferred embodiment of the present invention, the reference numerals 1 to 10 generally consecutively designate successive lenses from the front lens 1 on the object side to the rear lens 10 on the image side. The second lens 2 is air spaced from first lens 1 and third lens 3 is air spaced from second lens 2. The successive third, fourth and fifth lenses, 3, 4 and 5 are cemented at their respective confronting mating faces to form a first positive triplet lens subsystem and the successive sixth, seventh and eighth lenses 6, 7 and 8 are cemented at their respective confronting mating faces to form a positive second triplet lens subsystem. The ninth lens 9 is air spaced from the eighth lens 8 and the th lens 10 is air spaced from the ninth lens 9.

The first lens 1 is a negative meniscus lens of thickness d index of refraction n,, Abbes number 11 with a convex front surface 8 of radius of curvature r and a concave rear surface S of radius of curvature r less than r,. The second lens 2 is a meniscus lens of lesser power than lens 1 and is of thickness d index of refraction N Abbes number 11 with a convex front surface S of radius of curvature r and spaced from surface S at distance d and a concave rear surface S of radius of curvature r... The third lens 3 is a positive biconvex lens of thickness d index of refraction N and Abbes number 11,, with a front surface S, of radius of curvature r spaced a distance d from surface S and a rear surface ative biconcave lens of thickness d,;, index of refraction N and Abbe 's number 11 with a front face mating and cemented to surface S and a rear surface S, of radius of curvature r,. The fifth lens 5 is a positive lens of thickness d,, index of refraction N and Abbe 5 number v with a front face mating and cemented to surface S and a rear surface of radius of curvature r The sixth lens 6 is a negative lens of thickness d index of refraction N and Abbes number 11 with a front surface S of radius of curvature r and spaced a .distance d from surface S and a rear surface S of radius of curvature r The seventh lens 7 is a doubly convex positive lens of thickness d index of refraction N and Abbe s number 11 with a front face mating and cemented to surface S and a rear surface S of radius of curvature r and the eighth lens 8 is a negative lens of thickness d index of refraction r and Abbes number 11 with a front face mating and cemented to surface S and a rear surface S of radius of curvature r The ninth lens 9 is a negative meniscus lens of thickness d index of refraction N and Abbes number 11 with a concave front surface S of radius of curvature r spaced from surface a distance 41, and a rear surface S,., of radius of curvature r and greater than r The 10th lens 10 is a negative lens of less power than ninth lens 9 and is of a thickness (1, index of refraction N and Abbes number u and has a front surface S of radius of curvature r and spaced a distance d from surface S and a rear surface S of radius of curvature The following Table l sets forth as specific example of the improved lens system by way of illustration, the

radii of curvatures r, of the lens surfaces S to S the 7 distance d, between each surface S, and the next successive surface S the distances being lens thicknesses or air spaces and are measured along the optical axis, m the d-line index of refraction of the i th lens and v, the Abbes number of the ith lens. The lens system has a focus F 100, it being understood that the radii r, and the distances d,- may be proportionately changed for changes in lens system focal length F. Also set forth are the focal lengths F F and F of lenses 1, 2 and 10, F the focal length of lens 1 and 2, F, the focal length of the lens subsystem including lenses 1 through 8 and F the focal length of the subsystem including lenses 1 through 9.

S of radius of curvature R The fourth lens 4 is a neg- The following Table ll sets forth the Seidels coefficients for the lens system set forth in Table 1.

mm a e m s u m c n O c g fifth lenses are joined at their matin to form a first triplet sub-system and the sixth and eighth lenses are joined at their matin faces to form a second tri 5 the following dimensions a g .mm mm h r.

01 d on a m 6 t S y.- b ulm a MV V l d p n 749 332455 50 l 232 000550 0 3 II The highly superior optical properties and performi th radi s of curvature f the jth lens ance of the lens System Set forth in Table I are demonmating confronting lens faces definstrated by the group of aberration curves of this lens ihg a single surface dJ is the distance between the system as illustrated in FIGS. 2(a) to 2(d). jth Surface and the surface wherein r surface,

the surfaces being While there has been described and illustrated in preconsecutively designated from the front to the rear ferred embodiment of the present invention, it is apparlens surface, d, is the distance between the jth surface and the j-H surface,

ent that numerous alterations and additions may be made without departing from the spirit thereof.

the focal length F of the entire,

ge m 6 m v f am am y .m e S V bnu h w d n a n I claim:

equal to 100, N, is the d-line refra A Wlfle angle lens SXStem F pf lg ten consecu' ith lens and u, is the Abbes number of the ith lens. tlvely designated lenses m which the third, fourth and UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 33325321 Dated July 23, 1974 Invent r( Yasuo "Iakahashi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

-- [73] Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha,

Japan Signed and Sealed this twentieth Day of April1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnmissium'r nj'lurt'nts and Trademarks 

1. A wide angle lens system comprising ten consecutively designated lenses in which the third, fourth and fifth lenses are joined at their mating confronting faces to form a first triplet sub-system and the sixth, seventh and eighth lenses are joined at their mating confronting faces to form a second triplet subsystem and having the following dimensions and values: 